Process of chlorinating gaseous hydrocarbons and recovering products therefrom



urrso STATES PAENT CARBIDE &

CARBON CHEMICALS CORPORATION, A CORPORATION OF NEW YORK,

PROCESS OF CHLORINATING GASEOUS HYDROCARBONS AND RECOI no 'rnonnc'rs THEREFROHI.

No Drawing.

To all whom it may concern:

Be it known that I, GEORGE O. CURME, J r., a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Processes of Chlorinating Gaseous Hydrocarbons and Recovering Products Therefrom, of which the following is a specification.

This invention relates to the chlorination of such hydrocarbons as yield substitution products with chlorin or equivalent halogens when treated therewith in gaseous phrase; and to the separation and recovery of the reastion products, including the halogen aci An essential feature of my invention consists in efi'ecting the chlorination of the hydrocarbons in the gaseous phase and-under anhydrous conditions, and thereafter isolating from the reaction mixture the unchanged hydrocarbon, the chlorin derivatives thereof, and the halogen acid, or some of them, by liquefaction methods comparable to those applicable for the separation and recovery of the components of air or other mixtures of so-called fixed gases. By proceeding in this way certain highly important technical advantages are secured as hereinafter explained.- I will explain my process by reference to methane as atypical gaseous hydrocarbon yielding substitution products with chlorin; althaugh it is to be clearly understood that the process is applicable broadly to the halogenation in aseous phase of all hydrocarbon bodies of the nature above indicated. For example ethane may be treated in substantially the same manner, although the products thereby obtained have at the present time a decidedly lower industrial value.

In this connection it may be explained that the general procedure of chlorinating methane, or gases rich in methane, is one which has been carried out by many independent investigators under a great variety of operatin conditions. It has been thoroughly emonstrated that the four following reactions may be made to proceed Specification of netters Patent.

Patented July 118, 1922.

Application field July 7, 1920. Serial No. 394.571.

smoothly with the absence of the explosive side react1ons:

Also, by proper control of the proportion of chlorin used, any of the desired reactions may be made to predominate, although in no case, wlth the possible exception of the formation of carbon tetrachlorid, does any single reaction proceed to the exclusion of all others; for in every case certain quantities of all the other theoretically possible products are formed. In case carbon tetrachlorid is the desired product a practically theoretical yield may be obtained by using a suflicient excess of chlorin. In case any of the other derivatives is desired, more care must be observed in choosing the quantity of chlorin and also in controlling the other conditions of the reaction.v It is further to be noted that ethane or higher parafiins are much more easily attacked by chlorin than is methane; and accordingly an extensive waste of chlorin is caused by the presence of substantial proportions of these higher paralfins, which yield per-chlormated derivatives of little or no present industrial value, together of course with the equlvalent quantities of hydrochloric acid.

An examination of the equations (1) to (4) above shows that hydrochloric acid is one of the principal products of the reaction; and in order to operate economically this material must be recovered. By. the usual procedure this involves the rather difficult absorption in water, and results in the introduction of moisture into the gas mixture, which is thereby rendered unfit for direct re-use in the chlorinating process. Also, the meth l chlorid, being a very volatile substance (boiling point-24 O.) is very difficultly condensed from the large excess of'methane, even after the removal of the hydrochloric acid; and is therefore either partly wasted, or is returned to the system and undergoes chlor nat on o a h g er as natural gas or any stage. Under present commercial conditions, with an acute shortage of methyl alcohol and its derivatives, it is chiefly the lighter chlorinated derivatives of methane which are desired. Accordingly a high yield and good recovery of methyl chlorid and of'methylene chlorid are the principal desiderata in the successful operation of the present process. I

The present invention affords a minimum production of undesirable material, a maximum utilization of the chlorin, and a practically complete recovery of all of the products of reaction in a condition for easy commercial utilization.

A preferred embodiment of the invention is as follows:

Substantially pure methane is first 1S0- lated from any available gas mixture, such of the various industrial gas mixtures. This may be accomplished by a process essentially the same in principle as that now wldely employed for the separation and recovery of nitrogen, oxygen, argon, etc. from atmospheric air; that is to say by liquefaction and rectification, preferably in columns of the Llnde type. The methane is then mixed with suitable proportions, say 5 to 30% more or less, of chlorin, the proportion varymg according to the predominating product desired: and the mixture is passed at elevated temperatures rial, which in the preferred embodiment of the invention is so-called activated carbon prepared by the Chaney process. All materials entering into the reaction as well as the catalyst, should be moisture-free, under which conditions the entire operation, including the steps later to be described, may be carried out in iron orsteel apparatus. It will be understoodhowever that my invention is not restricted to any specific operating conditions during the chlorinating step.

In the preferred embodiment of the process the operation will be cyclical in character, in the sense that methane, substantially undiluted by nitrogen or other gases, will be repeatedly circulated .through the system including the catalyzer; the chlorinated products including the hydrochloric acid being substantially separated from the as mixture at each repetition of the cycle.

or this purpose dry methane and dry chlo-- rin are constantly supplied to the reacting system in the esired proportions, these gases, with a large excess of methane, being then continuously circulated through the catalytic chamber; thence through a watercooled condenser where heavier reaction products such as chloroform and carbon tetrachlorid are partly condensed; then compressed to several atmospheres pressure, andled through a heat exchanger into a liqueover any suitable catalytic mate-.

faction and rectification tower, preferably of the Linde type. In this tower the temperature is such that substantially all of the substances present with the exception of the methane (together with any nitrogen or air which may be incidentally present as impurities) are condensed and retained as a liquid mixture, the excess methane alone being carried in gaseous phase through the heat exchanger and used again in the same operating cycle. This procedure is made possible by the extremely low boiling point of methane (-165 C.) which is materially lower than that of any other component of the original reaction mixture. Small quantities of hydrochloric acid (boiling point -80 C.) may carry through with the methane in gaseous form, but this is generally unobjectionable, since the concentration is not large and cannot build up beyond a small equilibrium point.

The exact method of producing and maintaining this low temperature in the liquefaction and rectification tower is not material to the present invention, since several methods will readily suggest themselves to those skilled in this art, the Linde system being preferred.

The liquid mixture retained contains the follovtving substances in varying proportions, to wi Boiling point. Hydrochloric acid -80 C. Methyl chlorid 24: C. klfishylpne chlorid +42 C. oro orm ,+61 C. Carbon tetrachlorid- +78 Cl only then be collected and separated in any desired manner to recover each in a state of purity. The first of these procedures is now regarded as the more desirable, since it offers the possibility of producing liquid anhydr us hydrochloric acid, capable of being storedin steel cylinders, as a new article .of

commerce.

Both procedures present the great technical advantage that no moisture is brought into contact with the methane at any stage of the process, whereby as explained above, the cyclical repetition of the process in iron or steel apparatus is rendered possible.

It is to be understood that the process as described above is likewise applicable to the preparation of halogen compounds other than chlorin compounds, for example the halogens are to be regarded as the equivalents of chlorin for the purposes of this in-.

vention.

I claim 1. Process of preparing and recovering halogen substitution-products from gaseous hydrocarbons, comprising mixing the hydrocarbon in excess with the gaseous halogen; effecting combination of the halogen With liberation of the anhydrous halogen acid;

separating the reaction products of higher boiling point than the hydrocarbon from the resulting gas mixture by anhydrous liquefaction; and returning the residual gaseous hydrocarbon to the operating cycle.

2. Process according to claim' 1, wherein the resulting halogen products are fractionally separated from each other.

n testimony whereof, I aflix my signature.

GEORGE O. CURME, JR. 

